1. Field of Invention
The present disclosure relates to wireless data transmission with predictive transmission adjustments in an implantable hearing prosthesis such as cochlear implants, direct acoustic stimulation devices and middle ear devices.
2. Related Art
Typical implantable hearing prosthesis are semi-implantable and consist of an implantable part including a receiving coil and an external part. The external part may be a Behind-The-Ear (BTE) hearing aid device that houses a microphone, a speech processor, a transmitter and a battery. The BTE is connected to a transmitter coil and sends power and data to the implant via a transmitter coil. The transmitter coil and implanted receiving coil are positioned proximate to each other by two magnets.
The speech processor converts the analog signal of the microphone into encoded digital signals. The transmitter modulates a RF (radio frequency, e.g. 5 MHz) carrier with the encoded digital signal. The transmitter also comprises coil drivers for driving the transmitter coil based on the modulated RF carrier. The transmitter coil inductively couples to the implanted receiving coil so that both data and energy are transmitted into the implanted device. Thereby, the transmission path is designed to transmit energy and data as efficiently as possible, i.e. the transmission losses are as low as possible and the data integrity is as high as possible. The modulated RF carrier comprises a sequence of pulses, which may be pulse width modulated, frequency modulated or amplitude modulated. In the case of amplitude modulated carriers, the carrier may be, e.g., modulated by switching on and off selected pulses. Thereby, a predetermined number of on/off-switched pulses define a data symbol containing a predetermined amount of information. In any case of modulation type, the series of pulses define a stream of energy and information which is used by the receiver.
Due to band-pass limitations and the resonant nature of the transmission path, an effect occurs, generally known as intersymbol interference (ISI). Thus, in a sentence, the basic problem of such devices is intersymbol interference caused by the band-pass filtering effect of inductively coupled resonant circuits.